Biomedical Engineering Reference
In-Depth Information
(a) Checkers which did not fulfill the 50%-coverage rule but were still close to
a white square resulted in an error value of
05
(b) Checkers which were placed nowhere near a white square resulted in an
error value of
−
−
1
(c) White squares that were not covered resulted in an error value of
−
1
As before, Eq. 2 was used to calculate an average time to place one checker on
one white square. This average time was then multiplied by the error value of
each board and added to the measured time to obtain the Final Time.
The number of correctly placed checkers is denoted as percent correct for each
board and test subject. Percent correct is calculated using the following formula:
Number of correctly placed checkers
Number of white squares
Percent correct
=
×
100
(3)
The error scoring method under 2b above was introduced in experiment 3, when
we noticed that some subjects would cover all white squares but placed one or
more additional checkers on the board. For experiment 1, this rule had not been
necessary, as the test subjects did not place any additional checkers during the
tests, and no or few additional checkers were given to the subjects.
Experiment 1
In the first experiment, we introduced the test subjects to the experimental setup,
starting with boards on which the number of white squares was less than or equal
to three. The number of squares was then increased in
+
1 steps for the checker
placement task. Initially, the counting and checker placing tasks were combined
in such a way that the subject had to count the same number of white squares on
three different boards, and then would place the checkers, also three times. The
orientation of the boards was varied randomly to avoid recognition, and subjects
frequently did not realize that the number remained constant due to the difficulty
of the task. Subsequently, the difficulty level was increased by interjecting boards
with slightly different numbers of white squares during the counting task.
Checkers to be placed on the board were stacked on the side of the board corre-
sponding to the subject's handedness. The number of checkers available to the
subject depended on the number of white squares on the board: For boards with
a number of white squares less or equal to four, six checkers were placed next to
the board, and for boards with more white squares the number of checkers was the
number of white squares plus two. This approach was chosen to limit the possi-
bility of false placement. Only if the test subject was searching for more checkers
after placing all of them (and thus misplacing some of them) were more checkers
provided.
At the end of the first experiment, we asked the test subjects if they found
any connection between the number of white squares which they had counted
and the number of checkers they subsequently placed. Subjects unanimously
reported that they did not count the number of checkers they placed, and they
could not tell if there was a connection between the numbers.
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